Polyolefin fibers are known in the art. Polypropylene fibers are particularly attractive because of their low density, high melting point, inertness to a wide variety of inorganic acids and bases and organic solvents at room temperature and low cost. However, polypropylene fibers, like other polyolefins, are inherently difficult to dye and very susceptible to UV and thermal degradation.
To address some of these problems, polyolefin fibers have been prepared from polyolefin compositions containing grafted polyolefins. For example, U.S. Pat. No. 3,849,516 discloses incorporating into stabilized polyolefin compositions consisting of a polyolefin and conventional stabilizing additives, from 0.5 to 1 wt. % of a grafted polyolefin, such as acrylic acid grafted polypropylene, based on the total weight of the final blend, to decrease the amount of conventional stabilizers used in the composition.
In an attempt to improve the dye affinity of polyolefin fibers, polyolefin compositions have been blended with 1 to 50 parts by weight of graft copolymer having 0.1 to 20 wt. % of at least one alpha, beta-unsaturated carboxylic acid or anhydride thereof grafted onto a preformed polyolefin backbone, as disclosed in U.S. Pat. Nos. 4,732,571 and 4,872,880. The monomers disclosed are non-homopolymerizable monomers. According to another method, fibers are prepared from a monoethylenically unsaturated, heterocyclic, nitrogen-containing monomer either alone or together with one or more other ethylenically unsaturated monomers graft polymerized onto a polyolefin backbone using a particular diperester free radical initiator. This method is described in U.S. Pat. No. 3,644,581.
U.S. Pat. No. 4,957,974 discloses blends which exhibit improved melt strength, comprising a polyolefin and a graft copolymer consisting of a non-polar polyolefin trunk and at least 80% of a monomer of a methacrylic ester and less than 20% of an acrylic or styrenic monomer, wherein from 0.2 to 10% of the total formulation (polyolefin plus graft copolymer) is a chemically grafted acrylic polymer or copolymer.
However, none provide an improvement of the mechanical properties of the propylene polymer material in fiber form.